The aspect ratio defines the ratio of the width of a picture to its height. The aspect ratio of a commercial movie theater's screen is at least five to three, and the conventional U.S. television picture, as specified by the National Television Standards Committee (NTSC) is four to three. The difference between aspect ratios of a conventional television picture and commercial movie theater results in the loss of picture information when movies originally produced for viewing on a commercial movie theater screen are later transmitted for display on a conventional television set, since the television set is incapable of displaying all the information present in the original movie theater picture. Another problem that arises because of the four to three aspect ratio of conventional television is that certain production techniques make advantageous use of a wider screen for displaying scenes at a distance. In general, such production techniques require a higher definition picture than that that is presently available in conventional television.
An approach to providing high-definition television that could be received as a conventional television picture by conventional television receivers operating according to the NTSC standard or could be received as a high-definition television picture by newly designed receivers without requiring prohibitively large bandwidth is disclosed in an article entitled, "A Compatible High-Definition Television System", by T. S. Rzeszewski, The Bell System Technical Journal, Vol. 62, No. 7, September, 1983, pp. 2091-2111. In that system, one 6 megahertz (MHz) television channel carries the conventional information while the high-frequency luminance and high-frequency chrominance information are provided in a second 6 MHz television channel. That system has an aspect ratio of four to three. Whereas, for many applications the aspect ratio of four to three is suitable, there exists applications for which a greater aspect ratio is desired.
Therefore, there exists a need for a high-definition television system that is compatible with standard NTSC systems but that can also provide improved aspect ratio information without requiring a greater bandwidth than that provided by two television channels.